Stabilizing apparatus for ships

ABSTRACT

This invention relates to a stabilizing device for a ship. The device incorporates a hydrofoil formed with a chamber located close to the tip and passages leading from the chamber and debouching in the vicinity of the tip. The construction is effective to suppress cavitation.

United States Patent [151 3,688,726 Mitchell, deceased Sept. 5, 1972 [54] STABILIZING APPARATUS FOR SHIPS [56] References Cited [72] Inventor: Colin Campbell Mitchell, deceased, UNITED STATES PATENTS late of Edinburgh, Scotland, Andrew wishart and John Mello ..l X pattulo, h of Edinburgh, Scot- 3,221,698 12/1965 Turner ..1l4/66.5 H land, executors Primary ExaminerTrygve M. Blix [73] Asslgnee: Bmqlers m) Att0rney-Larson, Taylor and Hinds Lunlted, Edinburgh, Scotland 22] Filed: Nov. 3, 1969 t 7] ABSTRACT [21] A L N 373,435 This invention relates to a stabilizing device for a ship. The device incorporates a hydrofoil formed with a chamber located close to the tip and passages leading [30] Forelgn Apphcauon Pnonty Data from the chamber and debouching in the vicinity of Nov. 9, 1968 Great Britain ..53,190/68 the tip. The construction is effective to suppress cavitation. [52] US. Cl ..114/l26, 114/665 H 51 Int. Cl ..B63b 39/06, B63b 43/04 9 Chums 6 figures [58] Field of Search ..l14/126, 66.5 H, 166;

PATENTED SEP 5 I972 SHEET 2 0F STABILIZING APPARATUS FOR SHIPS This invention relates to stabilizing apparatus for ships and particularly to stabilizing apparatus of the type incorporating hydrofoils which may be fixed or may be movable to provide varying angles of incidence.

It is known that cavitation occurs at the tip of such a stabilizing device when it is in operation. Such cavitation gives rise to vortices which stream from the tailing edge of the stabilizing device. At best this situation results in the production of underwater noise and in extreme cases the vortices may extend far enough to be drawn into the stream of water entering the ships propeller thereby reducing the efficiency of the propeller and possibly causing erosion of the propeller.

Cavitation occurs when water streaming over the surface of the stabilizing device is unable to change direction fast enough to follow the contour of the stabilizing device and leaves the surface of the device to cause a cavity to be formed between the stream and the surface.

The problem is consequently to eliminate the conditions which cause cavitation during operation of a stabilizing device.

It is an object of the present invention to provide a construction of stabilizing device in which cavitation is eliminated or greatly reduced.

A stabilizing device according to the invention consists of a hydrofoil formed with an internal chamber at the tip and passages disposed in at least one fore and aft row leading from the chamber and debouching at the surface of the hydrofoil in the vicinity of the tip of the hydrofoil.

In one construction the hydrofoil is additionally formed with at least one entry port in the leading edge providing access to the chamber, and the passages lead from the chamber in a direction oblique and rearward with respect to the span of the hydrofoil (i.e. the fore and aft direction).

Preferably, the hydrofoil is formed with passages arranged in several rows.

Conveniently the hydrofoil may be formed in two portions, a main body portion and a tip portion connected to the main body portion, the tip portion being shaped as a hollow cap arranged to fit over the outer end of the main body portion and being formed with the entry port and the passages, the chamber being defined between the hollow cap and the adjacent end of the main body portion. The chamber in this construction may be. arranged to taper from a maximum width at the leading edge to a minimum width at the trailing edge.

The hydrofoil may be formed with several passages in several rows in tier formation, at least one row being of upwardly directed passages and at least one row being of downwardly directed passages debouching at intervals in a fore and aft direction along the upper portion and the lower portion respectively of the tip of the hydrofoil.

The hydrofoil may be formed with several entry ports in the leading edge of the hydrofoil. The or each port may be circular, elliptical, or in the form of a slot.

In an alternative construction the passages are arranged in several rows of which at least one row is disposed along the upper surface of the hydrofoil, at least one row is disposed along the under surface of the hydrofoil, and at least one row is disposed along the tip of the hydrofoil.

The chamber may be built as an extension on to the tip of a previously-existing hydrofoil. Where this is done the chamber may be constituted by an extension' of the upper surface of the previously-existing hydrofoil an extension of the under surface of the previously-existing hydrofoil and a new tip spaced from the existing tip of the previously-existing hydrofoil formed respectively by three appropriately shaped metal plates fastened to the existing hydrofoil and to one another as by welding. In this construction the passages may be constituted by holes drilled in the plates.

The hydrofoil may be a stationary or a movable fin or may be a bilge keel.

Practical embodiments of the invention are illustrated in the accompanying semi-diagrammatic drawings in which FIG. 1 is a plan view of a hydrofoil according to one embodiment of the invention,

FIG. 2 is .an elevation looking on the leading (adjacent) edge of the hydrofoil illustrated in FIG. 1 and FIG. 3 is an elevation looking towards the tip of the hydrofoil illustrated in FIG. 1;

FIG. 4 is a plan view of another embodiment of the invention,

' FIG. 5 is a section through 55 in FIG. 4, and

FIG. 6 is a view looking towards the tip of the hydrofoil illustrated in FIG. 4.

In the drawings, and referring first to FIGS. 1 to 3, 1 denotes the complete hydrofoil, 2. denotes an internal chamber formed within the hydrofoil, the leading edge 3 of the hydrofoil being formed with an entry port 4 providing access to the chamber 2 and the tip of the hydrofoil being formed with passages 5 leading obliquely and rearwardly with respect to the span of the hydrofoil and debouching at the tip of the hydrofoil through ports 6. The hydrofoil is formed in two portions of which one is a main body portion 1A and the other is a tip portion 7 formed as a hollow cap arranged to fit over the end of the main portion 1A and formed with the entry port and the passages, the hollow cap constituting the tip portion 7 defining with the main body portion 1A the chamber 2. The tip portion itself is formed for convenience of manufacture from two portions, a shell portion 7A and an outer tip portion 8 fixed to the shell portion 7A and formed with the passages 5. To avoid confusion the span of the hydrofoil is defined as the dimension 9.

Referring to FIGS. 4 to 6, the chamber 2 is formed by three plates l0, l1 and 12 welded to one another and to the tip of an existing complete hydrofoil 13 to form respectively extensions to the upper surface and the lower surface of the hydrofoil and a new tip to the hydrofoil. The plates 10, 11, 12 being formed with holes 14 constituting passages. It will be understood that although in this illustrated embodiment the chamber 2 is formed of several separate plates welded to one another and to the tip of an existing complete hydrofoil, the chamber may be formed as an integral unit which is then attached to an existing hydrofoil or the chamber may be built into the hydrofoil when the hydrofoil is being constructed.

In practice, and referring first to FIGS. 1 to 3 when the hydrofoil l is moving through the water, water enters the entry port 4 by reason of the forward movement of the hydrofoil, fills the chamber 2, is accelerated in its passage through the narrowing chamber and flows outwards through the passages 5 and the ports 6, and issues at increased velocity from the hydrofoil at the tip where cavitation tends to take place. The water issuing from the ports 6 fills the space which would otherwise be left empty at the point where the water flowing past the hydrofoil leaves the surfaces of the hydrofoil. Cavitation thus does not take place and no vortex is formed. The mode of action of the embodiment illustrated in FIGS. 4 to 6 is similar to that of the embodiment in FIGS. 1 to 3 except that water enters the chamber through some of the passages near the leading edge of the hydrofoil and leaves the chamber through the passages towards the trailing edge of the hydrofoil. The embodiment of FIGS. 1 to 3 is slightly more efficient hydrodynamically, but the embodiment of FIGS. 4 to 6 is easier and cheaper to construct and is easy to incorporate in an existing hydrofoil.

What is claimed is:

1. Astabilizing device comprising a hydrofoil formed with an internal chamber at the tip of the hydrofoil and passages disposed in at least one fore and aft row leading from the chamber and debouching at the surface of the hydrofoil in the vicinity of the tip of the hydrofoil and at least one entry port in the leading edge of the hydrofoil to provide access to the chamber, whereby fluids in the medium in which the hydrofoil is moving enters the said entry port as the said hydrofoil moves therethrough and leaves through the said passages to reduce cavitation in the vicinity of the tip.

2. A stabilizing device as claimed in claim 1 in which the passages lead from the chamber in a direction oblique and rearward with respect to the span of the hydrofoil.

3. A stabilizing device as claimed in claim 1 in which the hydrofoil is formed with passages arranged in several rows.

4. A stabilizing device as claimed in claim 3 in which the rows of passages are arranged in tier formation, the passages of at least one row being directed upwardly and debouching at intervals in a fore and aft direction along the upper portion of the tip of each hydrofoil,

and the passages of at least one other row being downwardly directed and debouching at intervals in a fore and aft direction along the lower portion of the tip of the hydrofoil.

5. A stabilizing device as claimed in claim 2 in which each hydrofoil is formed in two portions, a main body portion and a tip portion connected to the main body portion, the tip portion being shaped as a hollow cap arranged to fit over the outer end of the main body portion and being formed with the entry port and the passages, the chamber being defined between the hollow cap and the adjacent end of the main body portion.

6. A stabilizing device as claimed in'claim 5 in which the tip portion is constituted by a shell portion connected to the main body portion and formed with the entry port and an outer tip portion fixed to the shell portion and formed with the passages.

7. A stabilizing device as claimed in claim 2 in which the chamber tapers from a maximum width at the leadinedge to a minimum width at the trajlin edge.

. stabilizing device as claimed in c arm 1 incorporating several rows of passages in which at least one row is located along the upper surface of the hydrofoil, at least one row is located along the under surface of the hydrofoil, and at least one row is located along the tip of the hydrofoil.

9. A stabilizing device comprising a hydrofoil formed with an internal chamber at the tip of the hydrofoil and passages disposed in at least one fore and aft row lead- I ing from the chamber and debouching at the surface of the hydrofoil in the vicinity of the tip of the hydrofoil, said device comprising a previously existing hydrofoil and a chamber formed with passages fastened to the tip of the previously-existing hydrofoil, and wherein the chamber is formed of three appropriately shaped metal plates welded to one another and to the tip of the previously-existing hydrofoil, one plate constituting an extension of the upper surface of the previously-existing hydrofoil, another plate constituting an extension of the undersurface of the previously-existing hydrofoil and the remaining plate constituting a new tip for the stabilizing device spaced from the tip of the previouslyexisting hydrofoil. 

1. A stabilizing device comprising a hydrofoil formed with an internal chamber at the tip of the hydrofoil and passages disposed in at least one fore and aft row leading from the chamber and debouching at the surface of the hydrofoil in the vicinity of the tip of the hydrofoil and at least one entry port in the leading edge of the hydrofoil to provide access to the chamber, whereby fluids in the medium in which the hydrofoil is moving enters the said entry port as the said hydrofoil moves therethrough and leaves through the said passages to reduce cavitation in the vicinity of the tip.
 2. A stabilizing device as claimed in claim 1 in which the passages lead from the chamber in a direction oblique and rearward with respect to the span of the hydrofoil.
 3. A stabilizing device as claimed in claim 1 in which the hydrofoil is formed with passages arranged in several rows.
 4. A stabilizing device as claimed in claim 3 in which the rows of passages are arranged in tier formation, the passages of at least one row being directed upwardly and debouching at intervals in a fore and aft direction along the upper portion of the tip of each hydrofoil, and the passages of at least one other row being downwardly directed and debouching at intervals in a fore and aft direction along the lower portion of the tip of the hydrofoil.
 5. A stabilizing device as claimed in claim 2 in which each hydrofoil is formed in two portions, a main body portion and a tip portion connected to the main body portion, the tip portion being shaped as a hollow cap arranged to fit over the outer end of the main body portion and being formed with the entry port and the passages, the chamber being defined between the hollow cap and the adjacent end of the main body portion.
 6. A stabilizing device as claimed in claim 5 in which the tip portion is constituted by a shell portion connected to the main body portion and formed with the entry port and an outer tip portion fixed to the shell portion and formed with the passages.
 7. A stabilizing device as claimed in claim 2 in which the chamber tapers from a maximum width at the leading edge to a minimum width at the trailing edge.
 8. A stabilizing device as claimed in claim 1 incorporating several rows of passages in which at least one row is located along the upper surface of the hydrofoil, at least one row is located along the under surface of the hydrofoil, and at least one row is located along the tip of the hydrofoil.
 9. A stabilizing device comprising a hydrofoil formed with an internal chamber at the tip of the hydrofoil and passages disposed in at least one fore and aft row leading from the chamber and debouching at the surface of the hydrofoil in the vicinity of the tip of the hydrofoil, said device comprising a previously existing hydrofoil and a chamber formed with passages fastened to the tip of the previously-existing hydrofoil, and wherein the chamber is formed of three appropriately shaped metal plates welded to one another and to the tip of the previously-existing hydrofoil, one plate constituting an extension of the upper surface of the previously-existing hydrofoil, another plate constituting an extension of the undersurface of the previously-existing hydrofoil and the remaining plate constituting a new tip for the stabilizing device spaced from the tip of the previously-existing hydrofoil. 